1,592 research outputs found
An architecture for efficient gravitational wave parameter estimation with multimodal linear surrogate models
The recent direct observation of gravitational waves has further emphasized
the desire for fast, low-cost, and accurate methods to infer the parameters of
gravitational wave sources. Due to expense in waveform generation and data
handling, the cost of evaluating the likelihood function limits the
computational performance of these calculations. Building on recently developed
surrogate models and a novel parameter estimation pipeline, we show how to
quickly generate the likelihood function as an analytic, closed-form
expression. Using a straightforward variant of a production-scale parameter
estimation code, we demonstrate our method using surrogate models of
effective-one-body and numerical relativity waveforms. Our study is the first
time these models have been used for parameter estimation and one of the first
ever parameter estimation calculations with multi-modal numerical relativity
waveforms, which include all l <= 4 modes. Our grid-free method enables rapid
parameter estimation for any waveform with a suitable reduced-order model. The
methods described in this paper may also find use in other data analysis
studies, such as vetting coincident events or the computation of the
coalescing-compact-binary detection statistic.Comment: 10 pages, 3 figures, and 1 tabl
Coating thermal noise for arbitrary shaped beams
Advanced LIGO's sensitivity will be limited by coating noise. Though this
noise depends on beam shape, and though nongaussian beams are being seriously
considered for advanced LIGO, no published analysis exists to compare the
quantitative thermal noise improvement alternate beams offer. In this paper, we
derive and discuss a simple integral which completely characterizes the
dependence of coating thermal noise on shape. The derivation used applies
equally well, with minor modifications, to all other forms of thermal noise in
the low-frequency limit.Comment: 3 pages. Originally performed in August 2004. Submitted to CQG. (v2)
: Corrections from referee and other
Reactions at Polymer Interfaces: Transitions from Chemical to Diffusion-Control and Mixed Order Kinetics
We study reactions between end-functionalized chains at a polymer-polymer
interface. For small chemical reactivities (the typical case) the number of
diblocks formed, , obeys 2nd order chemically controlled kinetics, , until interfacial saturation. For high reactivities (e.g. radicals) a
transition occurs at short times to 2nd order diffusion-controlled kinetics,
with for unentangled chains while and
regimes occur for entangled chains. Long time kinetics are 1st order and
controlled by diffusion of the more dilute species to the interface: for unentangled cases, while and regimes
arise for entangled systems. The final 1st order regime is governed by center
of gravity diffusion, .Comment: 11 pages, 3 figures, uses poliface.sty, minor changes, to appear in
Europhysics Letter
The dependence of test-mass thermal noises on beam shape in gravitational-wave interferometers
In second-generation, ground-based interferometric gravitational-wave
detectors such as Advanced LIGO, the dominant noise at frequencies
Hz to Hz is expected to be due to thermal fluctuations in the
mirrors' substrates and coatings which induce random fluctuations in the shape
of the mirror face. The laser-light beam averages over these fluctuations; the
larger the beam and the flatter its light-power distribution, the better the
averaging and the lower the resulting thermal noise. In semi-infinite mirrors,
scaling laws for the influence of beam shape on the four dominant types of
thermal noise (coating Brownian, coating thermoelastic, substrate Brownian, and
substrate thermoelastic) have been suggested by various researchers and derived
with varying degrees of rigour. Because these scaling laws are important tools
for current research on optimizing the beam shape, it is important to firm up
our understanding of them. This paper (1) gives a summary of the prior work and
of gaps in the prior analyses, (2) gives a unified and rigorous derivation of
all four scaling laws, and (3) explores, relying on work by J. Agresti,
deviations from the scaling laws due to finite mirror size.Comment: 25 pages, 10 figures, submitted to Class. Quantum Gra
Accurate and efficient waveforms for compact binaries on eccentric orbits
Compact binaries that emit gravitational waves in the sensitivity band of
ground-based detectors can have non-negligible eccentricities just prior to
merger, depending on the formation scenario. We develop a purely analytic,
frequency-domain model for gravitational waves emitted by compact binaries on
orbits with small eccentricity, which reduces to the quasi-circular
post-Newtonian approximant TaylorF2 at zero eccentricity and to the
post-circular approximation of Yunes et al. (2009) at small eccentricity. Our
model uses a spectral approximation to the (post-Newtonian) Kepler problem to
model the orbital phase as a function of frequency, accounting for eccentricity
effects up to at each post-Newtonian order. Our approach
accurately reproduces an alternative time-domain eccentric waveform model for
eccentricities and binaries with total mass less than 12 solar
masses. As an application, we evaluate the signal amplitude that eccentric
binaries produce in different networks of existing and forthcoming
gravitational waves detectors. Assuming a population of eccentric systems
containing black holes and neutron stars that is uniformly distributed in
co-moving volume, we estimate that second generation detectors like Advanced
LIGO could detect approximately 0.1-10 events per year out to redshift , while an array of Einstein Telescope detectors could detect hundreds of
events per year to redshift .Comment: 12 pages, 6 figures, 1 appendix. Submitted to Phys. Rev. D. v2:
affiliations updated, one reference corrected. Accepted to Phys. Rev.
Connexin communication compartments and wound repair in epithelial tissue
Epithelial tissues line the lumen of tracts and ducts connecting to the external environment. They are critical in forming an interface between the internal and external environment and, following assault from environmental factors and pathogens, they must rapidly repair to maintain cellular homeostasis. These tissue networks, that range from a single cell layer, such as in airway epithelium, to highly stratified and differentiated epithelial surfaces, such as the epidermis, are held together by a junctional nexus of proteins including adherens, tight and gap junctions, often forming unique and localised communication compartments activated for localised tissue repair. This review focuses on the dynamic changes that occur in connexins, the constituent proteins of the intercellular gap junction channel, during wound-healing processes and in localised inflammation, with an emphasis on the lung and skin. Current developments in targeting connexins as corrective therapies to improve wound closure and resolve localised inflammation are also discussed. Finally, we consider the emergence of the zebrafish as a concerted whole-animal model to study, visualise and track the events of wound repair and regeneration in real-time living model systems
Kinetic Regimes and Cross-Over Times in Many-Particle Reacting Systems
We study kinetics of single species reactions ("A+A -> 0") for general local
reactivity Q and dynamical exponent z (rms displacement x_t ~ t^{1/z}.) For
small molecules z=2, whilst z=4,8 for certain polymer systems. For dimensions d
above the critical value d_c=z, kinetics are always mean field (MF). Below d_c,
the density n_t initially follows MF decay, n_0 - n_t ~ n_0^2 Q t. A 2-body
diffusion-controlled regime follows for strongly reactive systems (Q>Qstar ~
n_0^{(z-d)/d}) with n_0 - n_t ~ n_0^2 x_t^d. For Q<Qstar, MF kinetics persist,
with n_t ~ 1/Qt. In all cases n_t ~ 1/x_t^d at the longest times. Our analysis
avoids decoupling approximations by instead postulating weak physically
motivated bounds on correlation functions.Comment: 10 pages, 1 figure, uses bulk2.sty, minor changes, submitted to
Europhysics Letter
- …